The instant invention relates to non-corrective (non-prescription) lenses for use as sun lenses or safety lenses.
It is well known in the art that piano (non-corrective) sun lenses and safety lenses have convex and concave optical surfaces that are designed according the Gullstrand formula (See FIGS. 1A and 1B). For a spherical shape lens, the Gullstrand formula allows the designer to calculate the value of the concave side radius knowing the convex side radius, the thickness of the lens and the refractive index of the material. When using the Gullstrand formula for lens design, it is understood that the concave radius and convex radius are constant throughout the arc of the lens, but that the centers of the spheres or circles are slightly offset from one another, the offset being equal to the inner radius plus the thickness of the lens less the external Radius. The offset provides the lens with a shape wherein the lens is slightly thicker at the optical center, tapering to thinner at the outer edges. This thinning shape is obvious from the lenses illustrated in FIGS. 1A and 1B.
Such a lens, designed according to the Gullstrand formula gives good results and comfortable vision when the wearer of the eyewear is looking through the optical axis of the lens or in a direction parallel to the optical axis, i.e. generally forward vision looking straight ahead (See FIG. 1A). The optical axis is defined by the line passing through the centers of the two spheres defining both sides of the lenses. However, when the wearer is looking through the periphery of the lens, i.e. either laterally, or upwardly or downwardly, vision suffers from astigmatism, prism or other distortions of the vision.
The Gullstrand formula applies not only to spherical lenses but also to toric lenses (2 curvature radiuses according 2 perpendicular meridians for each side of the lens).
Cylindrical lenses are also considered as particular toric lenses having the vertical meridian with a radius R=∞. The optical aberrations discussed hereinabove are also visible on these lenses as well.
It is also known in the art that the visual axis may be offset from the optical axis as shown in the U.S. Pat. No. to Rayton No. 1,741,536. Such a lens as shown in Rayton generally improves vision in the main visual axis and particularly improves prism deviation. See also FIG. 1B of the drawings which illustrates an offset visual axis in a conventional Gullstrand lens.
In recent years, other developments have also been made in order to improve peripheral vision in both non-corrective and corrective lenses. For example, U.S. Pat. No. 6,129,435 (to Nike) describes a decentred low minus power lens that is intended to improve peripheral vision. This lens offsets the visual axis from the optical axis as previously known and further provides a low minus power to improve optical quality in the center portions of the lens. U.S. Pat. No. 6,361,166 (to Sola) describes an ophthalmic (corrective) lens with different optical zones that improve peripheral vision and avoid prismatic jump when scanning from one optical zone to another optical zone. U.S. Pat. No. 5,604,547 (to Gentex) describes a one-piece wide-field lens having aspheric and atoric (non-circular) inner and outer surfaces (in the horizontal meridian) that allow for good peripheral vision.
It is thus an object of the present invention to improve peripheral vision and astigmatism generally in the case of spherical and torical lenses which are both used in safety and sunglass lenses. The invention may be applied to spherical, cylindrical or torical shields or any shape that would cover one or both eyes. The invention will describe lens blanks whose designs do not show any optical axis whereas in the prior art, the lenses continue to utilize the optical axis.
The present invention aims to improve peripheral vision in the case of spherical lenses, cylindrical and toric lenses, and as an extension of the invention may be applied to any shape (free form). More specifically, the preferred embodiment of the instant invention provides a unique method for modifying the shape of a non-corrective lens such that astigmatic power is reduced throughout the lens and peripheral vision is improved. When the inventive method is applied, for example, to a torical shape, the method will not modify the general torical shape of the lens, but rather only one or both of the surfaces in such a way that the general Gullstrand shape is not changed.
The inventive method may generally be described as follows:
(I) The convex and concave sides of the lens are initially designed according to the Gullstrand Formula.
(II) Thereafter, a visual center of the lens is defined. The location of the visual center is preferably offset from the optical center of the lens. However, an offset location is not necessarily required according to the invention. Generally speaking, the offset of the visual center is determined by the need of the frame customer. Parameters such as base curve, front face angle of the frame, the size of the glazed lens, the distance between left and right lens frame, and the temple span allow the frame manufacturer cut the lens to locate the visual center in proper position in the frame. Accordingly, the visual center of the lens can be specifically designed for glazing in a particular frame.
In the case of the preferred toric lens blank (approximately Base 10/4.5) as will be described in detail herein, the visual center of the lens is preferably shifted along the X axis (horizontal meridian) between about 10 mm to about 25 mm, and preferably about 17 mm. This defines a visual axis (VA) that is parallel to the optical axis (OA) but offset to one side thereof. An additional vertical offset is also possible within the scope of the invention.
(III) Once the visual center is defined, the inner Gullstrand surface (concave surface) of the lens is modified so as to improve optical quality in the area where the visual center of the lens is defined as well as in other areas of the lens around the visual center. Modification of the inner Gullstrand surface is accomplished by first defining the inner surface as a set of reference points (along z-axis) relative to a reference plane (x-y), and then selectively adjusting the position of those reference points (along the z-axis) relative to the reference plane. In other words, the positions of the reference points (or localized groups of reference points) are shifted (along the z-axis) either towards or away from the x-y reference plane, with the effect of thickening or thinning the lens at those points and thus modifying the optical properties of the lens in those selected areas. By changing the values of these reference points, the inner surface is modified in order to improve optical quality, and particularly astigmatism in the main vision axis, but also in the peripheral area.
Improvement in optical quality is initially predicted and tested using three-dimensional modeling software that simulates the impact of light beams through the lens on the retina. The results of this software modeling identifies areas of the lens which have optical aberrations, and allows the lens surfaces to be modified until the aberrations are minimized or eliminated.
It is important to note that the process of defining the inner surface as a set of reference points (rather than radial values) allows the modified inner surface to be described as NURBS surface within a 3-D CAD (computer aided drafting) system. The localized modifications of the inner lens surface as required to improve optical quality, destroy the normally constant radial dimensions of the inner lens surface, and prevent the modified surface from being described by conventional radial dimensions. In the context of making the lenses in a molding process, this would normally prevent the lens surface from being accurately defined in a 3-D CAD system and would prevent automated milling of a mold surface in a computer aided milling (CAD-CAM) machine. However, by defining the inner surface using a NURBS reference system, the surface can now be accurately described and defined within a 3-D CAD system, and that information transferred to a computer aided milling (CAM) machine to produce the corresponding mold surface.
As a result, the lens or shield according to the invention has no optical center as it is defined by at least one surface that has no radius on any meridian. Instead of being defined by the position of the optical center, the lens according to the invention will be defined by the position of the visual center and the orientation the lens will have on the face of the wearer. The original optical axis (prior to modification) is changed to a Reference Axis (RA) and will be provided to the frame manufacturers in order to help frame manufacturers give the lens the proper orientation for glazing.
In other embodiments of the invention, it is possible to modify both the concave and convex surfaces so as to further improve optical properties while still-maintaining the general spherical, toric or cylindrical shape of the lens.
Accordingly, among the objects of the instant invention are:                the provision of a non-corrective lens having improved peripheral vision, and        the provision of a method of defining a non-corrective lens having improved peripheral vision.        
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.